Drought's Positive Effect: Smaller Gulf Dead Zone

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Though the parched conditions have wreaked havoc on natural
habitat and agricultural crops, drought may have one upside,
bringing the fourth smallest dead zone in the Gulf of Mexico
since mapping of this annual oxygen-free zone began in 1985.

Scientists estimate the 2012
Gulf of Mexico dead zone spans an area of 2,889 square miles
(7,482 square kilometers), or just larger than the state of
Delaware.

"The smaller area was expected because of drought
conditions and the fact that nutrient output into the Gulf
this spring approached near the 80-year record low," Nancy
Rabalais, executive director of the Louisiana Universities Marine
Consortium (LUMCON), said in a statement. Rabalais led the survey
cruise that measured the dead zone.

In fact, the last time the dead zone was this small was in 2000
when it measured 1,696 square miles, or 4,393 square km.

The number is also well below the 2011 dead zone, which reached
6,770 square miles (17,534 square km) as a result of floods that
carried loads of nutrients into the water. Scientists
recorded the smallest dead zone, at 15 square miles (39 square
km), in 1988, while the largest zone occurred in 2002 and covered
an 8,400-square-mile (21,756-square-km) swath.

Estimates for this dead zone, which forms each summer off the
coasts of Louisiana and Texas, are important because the loss of
oxygen can be dire for the animals that live there; the dead zone
also threatens commercial and recreational fishing in the Gulf.

The lack of oxygen results from nutrients,
particularly nitrogen, that run off the land, from
agricultural and other human activities, down the Mississippi
River and into the Gulf of Mexico. These nutrients are food for
algae, which grow as a result, before dying, sinking to the sea
bottom and decomposing. It's this decomposition that sucks all
the life-giving oxygen from the surrounding waters. [ Mightiest
Floods of the Mississippi River ]

Two groups of researchers had forecast earlier this summer
two very different potential sizes for this hypoxic zone, one
on the small side and the other more in line with an average-size
dead zone. The more conservative prediction, which involved
researchers at the University of Michigan, took into account the
nutrient-rich agricultural run-off from the Mississippi River
watershed this spring. The "average" prediction accounted for
leftovers from the prior year's nutrient pollution, called a
carryover effect.

The new estimate for the zone's small size suggests this
carryover effect on hypoxia was limited due to the drought (low
flow) conditions, the researchers noted.

Researchers at Texas A&M plan a follow-up cruise in
mid-August to provide an update on the dead-zone size.

The new research was supported by the National Oceanic and
Atmospheric Administration (NOAA).